Tethys is a satellite of Saturn. It was discovered by Giovanni Domenico Cassini in 1684. It has a nearly circular equatorial orbit at 294,660 km from the planet's centre. Its diameter is 1,060 km and its density is 1,200 kg/m3, indicating a predominantly icy composition. All parts of its surface are heavily cratered. Two outstanding topographic features are the giant Odysseuscrater, 400 km in diameter, and a trench or large valley, Ithaca Chasma, about 100 km in width and several kilometres deep. Research Tethys